During the injection molding of the plastic material devices one may, concurrently, provide components to be simultaneously injection molded, for example metallic components to enhance the mechanical stability, hooks, hinges and the like. Further, it is well-known in the art to injection mold so-called smart cards, i.e. plastic material cards having a module embedded therein. The module is inserted into the cavity of an injection molding machine mold prior to injecting the molten plastic material into the cavity. The term "module" is to be understood to comprise e.g. a semiconductor chip having, for example, an electric contact surface area being accessible from the outside of the card and serving to establish a single transmission line between the semiconductor chip and a card reading apparatus.
German patent specification 41 15 208 discloses a mold for manufacturing smart cards. Smart cards are flat devices of e.g. 50 mm width and 80 mm length and having a thickness of only about 0.6-0.8 mm. If an appropriately dimensioned cavity is provided in a plastic material injection molding mold, problems may arise due to the very narrow cross section because there might be a problem for the liquified or molten plastic material to propagate through the cavity with its very narrow cross-sectional area. This holds true the more when the extremely flat hollow cavity is, further, partially occupied by the module, the thickness of which being only a little smaller compared to the height of the cavity. If, for example, the module has a thickness of 0.6 mm and the inner height of the hollow cavity is 0.8 mm, the remaining free space "behind" the module is just a very narrow air gap of 0.2 mm width which does not allow an effective flow of the liquid plastic material.
The method and the apparatus disclosed in German patent specification 41 15 208 utilizes another approach. This prior art mold uses two piston-like plungers which are reciprocally operated. The plungers run in bores ending in a surface of the cavity. In the initial position the front faces of the plungers are essentially flush with that cavity surface. Therefore, in this initial position the molten plastic material may freely be injected into the practically unobstructed cross section of the hollow cavity. As long as the plastic material is still deformable, one of the plungers is advanced into the plastic material whereas the other stamp is retracted. The displacements and cross sections of the plungers are dimensioned such that during the movement of the plungers no change in volume occurs. Accordingly, when the plastic material has solidified and the device is ejected, it has a depression on that side where the first plunger had been advanced. This depression may be used for inserting a module in a subsequent operation, for example by gluing the module in place, after the plastic material device had been ejected from the mold.
It is, however, an inherent disadvantage of this prior art method that for mounting a module in the plastic material device a separate operational step is required after the unmolding of the device.
German disclosure document 41 42 410 discloses a method for producing flat plastic material devices, for example identification cards. This prior art device comprises two mold sections. The lower mold section has a prismatic, i.e. trapezoidal cross section. The lateral inclined surfaces are provided with flat hollow cavities having the shape of the identification cards to be produced. A second mold portion may be placed on top of the first mold portion, thus entirely covering the prismatic section. Moreover, channels are provided for injecting molten plastic materials into the hollow cavities.
Within the first mold portion bores are provided ending under right angles in the flat hollow cavities. Piston-like plungers run in these bores for feeding a module in a lateral direction to the hollow cavity. This is made by first retracting the plunger into an initial position and then again advancing the plunger which subsequently runs against a carrier sheet for stamping a module from that carrier sheet. While this is done molten plastic material is injected into the hollow cavity to replete same. By further advancing the plunger with the stamped-out module on top, the latter may be pressed into the liquid plastic material which is not yet solidified.
It is a disadvantage of this prior art apparatus that in view of the tolerances required to let the plunger run within the bore a small gap must be provided between the plunger and the surrounding bore surface. However, considering that the molten plastic material is injected under extremely high pressure, molten plastic material will also penetrate into the gap, the more as the pressure within the hollow cavity is still increased when the module is pressed into the liquid material which is not yet solidified. Therefore, when the plastic material is solidified and the plunger is retracted, the corresponding surface of the identification card has a small bulge around the module. The bulge is configured by the plastic material which has penetrated into the gap between the plunger and the bore. The bulge may be seen and felt by the user so that the identification card is defective insofar.
The prior art apparatus has the further disadvantage that due to the high pressure that prevails within the hollow cavity during the injection of the molten plastic material the plunger with the module resting on its front face may even be pressed back into the bore. As a result, the module will protrude from the corresponding surface of the identification card when the card has been produced.
Another similar process and apparatus are disclosed in German disclosure document 41 42 392.
It is, therefore, an object underlying the invention to provide a process and an apparatus of the kind mentioned at the outset which obviates the above-discussed disadvantages. In particular, it shall be possible to produce an entirely smooth, high-quality surface of the composite device, in particular a smart card.